Chick embryo cells (CEC) infected and morphologically altered by strain MC 29 avian leukosis virus, an agent capable of rapid and uniform morphological alteration of CEC in vitro, as well as the induction of a variety of neoplasms in vivo, will be studied with particular regard to viral-induced surface antigenic alterations. Antiviral and anticellular immune globulins labeled with fluorescein isothiocyanate will be used for localization of new antigens with quantitation of antigenic change being done by complement fixation. Ultrastructural localization of antigens will be done by immunoelectron microscopy. Studies will then be extended to the isolation and characterization of these antigens. Specific immune sera will be prepared against the isolates and tested for possible application in immunotherapy in the avian model.